Viscous damping (VD) was included in the PCF model as an additional stress term proportional to the elastic strain rate [1]}, \(\mathbf {\sigma }_{\text{VD}}=\mathbf {\eta }:\frac{\partial \mathbf {S}}{\partial t}\) , where \(\mathbf {\eta }\)  is known as the fourth-rank viscosity tensor. The mechanical wave equation is then written as:
\(\tilde{\nabla } \cdot (\mathbf {c}^{\prime }: \mathbf {S})=-\rho \Omega ^{2} \mathbf {u},\) 
